Programmable optical component for spatially controlling the intensity of beam of radiation

ABSTRACT

A programmable optical component ( 10 ) for spatially controlling the intensity of a beam of radiation (b), which component comprises a programmable layer which is divided in programmable elements ( 4,6,8 ), characterized in that each programmable element comprises bendable nano-elements ( 8 ) which are switchable between a non-bend state ( 8 ) and a bend state ( 8 ′) by means of a driver field. In their bend state the nano-elements absorb radiation. The programmable element may be a switchable diffraction grating or a programmable mask.

The invention relates to a programmable optical component for spatiallycontrolling the intensity of a beam of radiation, which componentcomprises a programmable layer, which is divided in programmableelements. The invention also relates to an optical scanning devicecomprising such a component and to a lithographic process wherein such acomponent is used.

Spatially controlling is understood to mean both controlling theintensity of discrete portions of a beam of radiation incident on theelement and controlling the propagation direction of radiation from thebeam.

An example of a programmable optical component is a switchablediffraction component, i.e. a diffraction element that can be set in anon-state and off-state, whereby in the off-state the diffraction layer,i.e. the programmable layer, forms a plane parallel layer. Anotherexample of a programmable optical component is programmable mask, forexample a lithographic mask.

A well-known diffraction component is an optical diffraction grating,which is widely used in the optical field, either as stand-alone elementor integrated with other optical components. A diffraction gratingsplits an incident beam into a, non-deflected, zero order sub-beam, apair of deflected first order sub-beams and pairs of sub-beams, whichare deflected in higher diffraction orders. There are two main typesdiffraction grating: amplitude gratings and phase gratings. An amplitudegrating comprises grating strips, which absorb incident radiation andalternate with intermediate strips, which transmit or reflect incidentradiation. A phase grating introduces a phase, or optical path length,difference between beam portions incident on grating strips and beamportions incident on intermediate strips, because the grating stripshave another refractive index or are situated at another level than theintermediate strips.

In view of new applications, for example in miniaturized flexibleoptical devices or in the optical recording technology, there is asteadily growing demand for diffraction gratings, which are easilyswitchable and preferably have a substantially smaller grating periodthan conventional gratings.

Optical lithography is a technology to print a design pattern in a layerof a substrate to configure said layer with device features. Thistechnology is used for manufacturing a device, which comprises usually anumber of such configured layers, which layers together provide therequired functionality's of the device. The device may be an integratedcircuit (IC), a liquid crystalline display (LCD) panel, a printedcircuit board (PCB) etc. Conventional optical lithography uses a photomask comprising a pattern corresponding to the pattern of features to beconfigured in the substrate layer, which mask pattern is imaged in aresist layer on top of the substrate layer by means of a lithographicprojection apparatus.

The manufacture of a photo mask is a time consuming and cumbersomeprocess, which renders such a mask expensive. If much re-design of aphoto mask is necessary or in case customer-specific devices, i.e. arelative small number of the same device, have to be manufactured, thelithographic manufacturing method using a photo mask is a costly method.There is thus a need for a mask the pattern of which can easily bechanged.

It is an object of the present invention to provide a programmableoptical component that can be used amongst others as a programmablegrating or in a flexible, in the sense of programmable, lithographicmask. This component is characterized in that that each programmableelement comprises bendable nano-elements, which all have their symmetryaxis substantially aligned in one direction which direction isswitchable between a non-bend state and a bend state by means of adriver field

The driver field may be an electrical field or a magnetic field,dependent on the nature of the bending elements. Substantially alignedin one direction is understood to mean that in principle the symmetryaxis of all nano-elements within a programmable element have the sameorientation or direction, said one direction, but that small deviationsof this one direction are possible, without effecting the opticalbehaviour of the programmable element. In case of a linear diffractiongrating the said one direction is parallel or perpendicular to thedirection of the grating strips.

Nano-element is a general term for nanotubes and nanowires, also calledwhiskers, and small prisms. Nano-elements are very small bodies having amore or less hollow (nanotubes) or filled (nanowires) cylindrical orprismatic shape having a smallest dimension, for example a diameter, inthe nano meter range. These bodies have a symmetry axis, the orientationof which determines electrical and optical properties, such as theabsorption characteristics of the material wherein they are embedded.When reference is made hereinafter to their orientation, this relates tothe orientation of their cylinder axis or prism axis.

Nano-elements have been described in several papers for a variety ofmaterials, such as indium phosphide (InP), zinc oxide (ZnO), zincselenide (ZnS), gallium arsenide (GaAs), gallium phosphide (GaP),silicon carbide (SiC), silicon (Si), boron nitride (BN), nickeldichloride (NiCL₂), molybdenum disulphide (MOS₂), tungsten disulphide(WS²) and carbon (C).

Particularly carbon nanotubes have been well studied. They are singlelayer or multiple layer cylindrical carbon structures of basicallygraphite (sp2-) configured carbon. The existence of both metallic andsemi-conducting nanotubes has been confirmed experimentally.Furthermore, it has been recently found that single walled carbonnanotubes (SWCNT) having a thickness of, for example 4-Angstrom alignedin channels of an AIPO₄-5 single crystal exhibit optical anisotropy.Carbon nanotubes are nearly transparent for radiation having awavelength in the range of 1.5 μm down to 200 nm and having apolarisation direction perpendiculaire to the tube axis. They showstrong absorption for radiation having a wavelength in the range of 600nm down to 200 nm and having a polarisation direction parallel to thetube axis (Li, Z. M. et al., Phys. Rev. Lett. 87 (2001),1277401-1-127401-4).

Similar properties have been found for nanotubes (or nanowires) otherthan those consisting of carbon. Nanotubes therefore most convenientlycombine the following features. They absorb radiation in a broad rangeof wavelengths depending on the orientation of the nanotubes relative tothe polarisation direction of said radiation and the orientation of thenanotubes can be directed and/or stabilised mechanically and/or by anelectrical or magnetic field.

A configuration of linear strips, which comprise nano-elements allhaving their symmetry axis aligned, i.e. in the same direction, whichstrip alternate with transparent intermediate strips, thus acts as anamplitude grating for linearly polarised light having its polarisationdirection perpendicular to the alignment direction.

In a similar way an optical component comprising a two-dimensionalpattern of areas, which are provided with aligned nano-elements(nano-elements areas), which areas alternate with transparent areas thuscan be used as a mask for linearly polarized radiation having itspolarization direction perpendicular to the alignment direction.

The present invention uses the fact that nano-elements can be modifiedchemically. For example, carbon nanotubes can be modified by athiolisation reaction, as described in the paper “OrganizingSingle-Walled Carbon nanotubes on Gold Using a Wet ChemicalSelf-Assembling Technique” by Z. Liu et al in Langmuir Vol. 16, No. 8(2000) p. 3569-3573. Thereby a self-assembled structure is obtainedwherein all carbon nanotubes are oriented perpendicular to the surface.The invention uses the insight that these nanotubes or nano-tubes or-elements of other materials can be bent along the field lines of adriver field, for example an electrical field produced by means ofelectrodes built-in in the programmable component. In a curved state,the nano elements are no longer parallel to the propagation direction ofthe incident radiation so that they absorb radiation having the properpolarization direction. If the driving field is switched off, thenano-elements resume their initial orientation, i.e. perpendicular tothe surface so that the same radiation can pass unhindered. In this way,portions of the programmable component, i.e. programmable elements canbe switched between a transparent and absorbing state and vice versa.

It is remarked that DE-A 100 59 685 discloses a device, which comprisesa substrate that is provided with a reflective or detecting surface andbendable elements, preferably carbon nanotubes. These nanotubes areconnected to a first electrode through direct attachment. If a voltageis supplied to a second electrode, which voltage is different from thevoltage on the first electrode and in the bendable elements, theseelements will bend their tips towards the second electrode. The elementsthen form a coating, which locally covers the surface so that thesurface locally becomes less reflective or less transmitting andportions of the beam are blocked. If the second voltage is removed fromthe second electrode, these beam portions are reflected or transmittedagain.

The voltage required for bending the nano-tubes in the known device isrelatively large, because the tubes should be bent more or lesscompletely, i.e. from an orientation perpendicular to the surface to anorientation substantially parallel to the surface, in order to locallycover the surface completely. Bending over large angles is possible onlyif the nanotubes satisfy high mechanical requirements.

The programmable component according to the invention differs in atleast three features and/or insights from the device of DE-A 100 59 685:

The nano-elements are transparent, at least to a large extent, iforiented substantially perpendicular to the substrate surface.Therefore, in the programmable component of the invention the bendablenano elements are arranged across a complete local surface portion thatshould be switched between the transparent state and the absorbingstate. In the known device the bendable elements are arranged only ontop of the electrodes and outside said surface portion in thetransparent state. Only if bent over a substantial angle they will coverthe surface portion.

In the programmable device of the invention use is made of the fact thatthe said surface portion becomes absorbing for radiation with the properpolarization direction even if the nano-elements within this portion arebent over a small angle only. In DE-A 100 59 685 the polarizationdependent behaviour of the nano-tubes is not mentioned.

In the programmable device of the invention the nano-elements do notform part of an electrode, but are arranged in an electrical or magneticfield between two electrodes. The physical principle governing thebehaviour of the nano-elements is their alignment to such a field, so asto obtain an energetically most favourable orientation.

In this way, the nano-elements need to be bent or curved to such degreethat they are partly disoriented with respect to the direction of theincident radiation. It is thus not necessary to bend the completely soas to cover a whole surface of a programmable element. In general thebend angle will in the range of 5° to 80°, preferably in the range of15° to 60° and most preferably in the range of 30° to 45°. The bendangle is defined in a plane determined by the propagation direction andthe polarisation direction of the radiation. Preferably, the propagationdirection is perpendicular to the substrate.

Since the bend angle is relatively small, less severe mechanicalrequirements have to be set to the nano-elements, which providessubstantial practical advantages. The nano-elements may be shorter thanin the known device and the adhesion of these elements is lessproblematic. The latter is due to, first of all, the reduced bend angleand secondly the reduced strength of the field required for bending thenano-elements. A lower force will be exerted on these elements,especially at the interfaces of these elements and the surface, whichinterfaces are mechanical weak portions.

Compared with the device of DE-A 100 59 685, the programmable componentof the invention provides two advantages. The first advantage is that itallows a high degree of miniaturization, because no space needs to bereserved for the nano-elements, because they are arranged across thewhole surface area of a programmable element. In the device of DE-A 10059 685 the nano-elements should be arranged outside the areas whichshould pass or block radiation, and the areas occupied by thenano-elements can not be used for other purposes. The second advantageis that the field strength of the driving field is considerably smaller.

With respect to its construction the programmable optical component ofthe invention may be further characterized in that it comprises asubstrate, an electrode configuration of first and second electrodeportions, which configuration defines the programmable element areas,and a nano-elements embedding medium on top of the electrodeconfiguration.

This is the simplest embodiment of the programmable component, which issuitable for most applications.

Preferably the programmable component is further characterized in thatan electrically isolating layer is arranged between the electrodeconfiguration and the nano elements embedding medium.

The isolating layer prevents electrical shorts and subsequent electricalcurrent flows, which may affect accurate controlled switching.Preferably the isolating layer is a dielectric layer.

Bending of the nano-elements is based on dipole interaction or onmagnetic interaction, dependent on the type of nano-elements. This isquite different from the electrostatic bending used in the device ofDE-A 100 59 685. For electrostatic bending the bendable elements shouldbe electrically connected to and preferably directly attached to theelectrodes. This introduces the risk of electrical shorts and of burningaway of the bendable elements, particularly if these elements consist oforganic material or if, for example carbon nanotubes are used.

The dielectric layer may comprise any inorganic or organic dielectricmaterial, such as aluminium oxide, silicon oxide, silicon nitride or aso-called high-K material.

The programmable optical component is preferably further characterizedin that the first and second electrode portions form a pair ofinterdigitated electrodes.

This allows high generating the electrical field with high efficiency.As the electrodes are interdigitated a channel is formed between them.The width of the channel may be small whilst at the same time thechannel may be very long. Thus, a relative low voltage is sufficient toprovide the electrical field strength (V/μm) required for bending.

If interdigitated electrodes are used, the direction of the nano-elementbending will not be the same at all locations; there will be bend angles+γ and bend angles −γ.

However, this has no consequences for the degree of absorption.

Preferably the programmable component is further characterized in thatthe electrode configuration is embedded in a planarizing layer and thenano-elements embedding layer is arranged on the planarizing layer.

The electrode configuration may be integrated with the substrate andcovered with a planarizing layer so as to provide a planer surface forthe nano-elements. The nano-elements embedding medium may be air, butpreference is given to a programmable component which is characterizedin that the nano-elements embedding medium is an insulating fluid.

Suitable fluids for this application are liquids, vapours and gases.Preferably the fluid is viscous to a certain extent so that it canprovide a counterforce. This allows a more accurate and mechanicallystabilized bending of the nano-elements. Another advantage of such afluid is that it prevents any sticking of the nano-elements to eachother. A person skilled in the art may adapt the fluid material andviscosity according to the specific application of the programmablecomponent.

In general, the bendable nano-elements will return to their initial,unbend position after removal of the electrical or magnetic field. Thisreturn may be influenced by the stiffness of the nano-elements and theiradhesion contact, i.e. the contact of the nano-elements with thesubstrate.

Return of the nano-elements to their initial, non-bent, state can beforced by reverting the orientation of the electrical or magnetic fieldduring a time period smaller than the period the field should be presentto set the nano-elements in the bent state. A forced return withoutfield reversion becomes possible if the programmable element ischaracterized in that a second electrode configuration is arranged atthe side of the nano-elements embedding medium remote from the mediumside facing the substrate.

Different types of nano-elements as defined in claims 8-13 may be usedin the programmable component. The nano-elements may be carbonnanotubes, metallic or semiconductor nanowires, metallic orsemiconductor nanotubes or magnetic nanowires or nanotubes filled withany (ferro-)magnetic material. The diameter of the nano-elements ispreferably less than 150 nm, more preferably, less than 50 nm andfurther preferably, between 0.3 nm and 10 nm. The length ofnano-elements is preferably in the range from 5 nm to 10 μm, morepreferably in the range from 10 to 500 nm and furthers preferably in therange from 50 to 300 nm.

Care should be taken that mutual screening of the nanowires issuppressed as much as possible. Mutual screening is the effect that oneof the nanowires within a given surface area attracts the major part ofthe local electrical field so that less electrical field remains for theother nanowires within this surface, i.e. the other nanowires areshielded form the field. In this aspect, semiconductor nanowires arepreferred to metallic nanowires, because they show less mutualscreening.

Nano-elements, particularly carbon nanotubes may be chemicallyfunctionalised so as to improve their attachment, or adhesion, to thesubstrate surface. In this way carbon nanotubes can be attached to agold surface, as described by Liu et al in the above cited paper inLangmuir. A suitable functionality for an oxide surface (SiO₂, Al₂O₃ orglass) is, for example SiCl₃ or Si(OR)₃, with R alkyl, preferablyisopropyl or butyl or phenyl. A suitable functionality for a goldsurface is a thiol or thiol-ether (Z-SH, Z-S—S-Z, Z-CH₂—S—CH₂-Z, with Zthe carbon nanotubes). A suitable functionality for a platinum surfaceis a base, such as —OH or —NH₂. A suitable functionality for a silver-or SiO₂ surface is an acid, such as —COOH. A suitable functionality fora non-oxidized silicon surface is a 1-ethylene-group (—CH═CH2). Asuitable functionality for a mica surface is a phosphide group or analkyldiphonic acid (PO₃ ²⁻).

Nanowires and nanotubes can also be produced by growing them in atemplate. The template allows defining the pattern of nano-elements inan easy and good-controllable way, as is described by Schönenberger etal. in J. Phys. Gem. B, Vol 101 (1997), 5497-5505. The template isprovided with pores which have a diameter preferably in the range from 3nm to 200 nm, more preferably in the range from 5 nm to 15 nm. Poreshaving uniform diameters can be produced with conventional techniques.The distance between the pores may be of the order from one to ten timesthe pore diameter. The pores may be substantially perpendicular to thesurface and be laterally ordered by providing suitable conditions or bylocal surface pre-treatment by means of for example an E-beam orimprinting. The nanowires can be grown by means of known methods, suchas electrochemical growth and the VLS (vapour-liquid-solid) method.Electrochemical growth of the nanowires is possible for III-V materials,II-VI materials and metals. The VLS method is suitable, for example, forIII-V materials and for carbon nanotubes and is generally performed attemperatures in the range from 400° to 800° C., as is known from thepaper of Morales and Lieber in Science, Vol 279 (1998), 208-211. Afterthe growth, the template is at least partially removed, for example, bymeans of wet- or dry etching.

Also alternative growth method can be used. Furthermore, nanowires maybe produced by etching a semiconductor substrate according to a requiredpattern. Anodic etching of a semiconductor substrate, particularly asilicon substrate, may be used to produce an array of a large number ofsemiconductor nanowires.

The programmable optical component may be further characterized in thateach nano-element is arranged in an insulating region.

In this embodiment no insulating layer between the electrodeconfiguration and the nano-elements is needed. The insulating regionscan be produced by using the VLS method and changing the gas compositionin the chamber during growth of the nano-elements. A growth processwherein process parameters are changed during the process is known assegmented growth.

The programmable component may be characterized in that it is atransmission component.

In this embodiment both the substrate and the electrode configurationshould be transparent. Transparent electrical conductive materials,which are suitable for the electrodes are very thin metal layers andparticularly oxide conductors, such as indium-tin-oxide (ITO), rutheniumoxide, lead ruthenium oxide (Pb₂Ru₂O₇), strontium lanthanum cobaltoxide, rhenium oxide and other materials, such as known from EP-A689294. Alternatively transparent electrically conductive organicmaterials, such as poly-(3,4-ethylenedioxy)thiophene (PEDOT) orpolyaniline (PAN) may be used.

Alternatively the programmable optical component may be characterized inthat it is a reflective component. Such a component may be the same as atransmission component, but has a reflective substrate or a reflectivelayer arranged between the substrate and the electrode configuration.

Depending on the shape and the pattern configuration of the programmableelements, the programmable component can be used for differentapplications. For a first application the component forms a switchablediffraction grating, wherein the programmable elements are elongated andconstitute grating strips, which alternate with nano-elements lessintermediate strips.

By switching the programmable elements on and off, the grating functioncan be set on and off. Such a switchable grating can be used in anapparatus, such as an apparatus for reading and/or writing an opticalrecord carrier, wherein two beams travel along a same path, whichcomprises a grating for only one of the beams.

The programmable grating may be a linear grating, wherein theprogrammable elements all extend in the same direction.

Alternatively the programmable grating may be a two-dimensional gratinghaving first programmable element extending in a first direction andsecond programmable elements extending in a second direction, differentfrom the first direction, which first programmable elements are arrangedin first surface areas and which second programmable elements arearranged in second surface areas alternating with the first surfaceareas.

Another type of programmable component according to the invention is aswitchable Fresnel lens, wherein the programmable elements have anannular shape and constitute Fresnel lens zones, which alternate withnano-elements less intermediate annular strips.

For another application the component forms a mask having a changeablemask pattern, wherein the programmable elements constitute pixels, whichare arranged in a two-dimensional structure.

By individually switching the programmable elements on and off anarbitrary mask pattern can be created. When using such a programmablemask in a process of manufacturing IC's or other devices by means oflithography, this process becomes flexible and very suitable forproducing devices in small quantities or customized devices.

The invention also relates to a device for scanning an opticalinformation carrier of a first type having a first information densityand an optical information carrier of a second type having a secondinformation density, which device comprises a radiation source unitsupplying a first radiation beam having a first wavelength forcooperating with the first type information carrier and a secondradiation beam having a second wavelength for cooperating with thesecond type of record carrier, and an objective system for focussing thefirst and second beam to a first and second scanning spot in theinformation layer of the first and second type information carrier. Thisdevice is characterized in that it comprises at least one diffractiongrating as described herein above.

This diffraction grating may be a beam-combining diffraction grating andmay be arranged in at least one of the following optical path portions:

between the radiation source unit and the objective system,

between the objective system and a radiation-sensitive detection systemfor receiving radiation from the information layers.

The diffraction grating may also be a three-spots diffraction grating,which is arranged between the radiation source unit and the objectivesystem.

The invention also relates to a lithographic process for producingdevice features in at least one layer of a substrate, which processcomprises transferring a mask pattern into the substrate layer by meansof a projection apparatus. This process is characterized in that use ismade of a programmable mask as described hereinbefore.

The projection apparatus is understood to mean an apparatus comprising aprojection system for imaging a mask pattern arranged at one side of theprojection system onto a substrate arranged at the other side of thissystem, but also proximity printing apparatus wherein the mask and thesubstrate are arranged close to each other.

These and other aspect of the invention will be apparent from andelucidated by way of non-limitative example with reference to theembodiments described hereinafter and illustrated in the accompanyingdrawings. In the drawings:

FIG. 1 shows a perspective view of a portion of a first embodiment of aprogrammable component according to the invention.;

FIG. 2 shows across-section of a programmable element of the componentwith the bendable nano-elements in their non-bended position;

FIG. 3 shows this element with the bendable nano-elements in theirbended position:

FIG. 4 a-4 e shows a cross-section of a second embodiment of theprogrammable component and some of the manufacturing steps;

FIG. 5 shows a diagram of a lithographic projection apparatus with aprogrammable mask according to the invention;

FIG. 6 shows a diagram of a device for scanning an optical recordcarrier, in which device one or more diffraction gratings according tothe invention may be used, and

FIG. 7 shows a Fresnel lens according to the invention.

The Figs. are not drawn to scale and are pure schematic. The samereference numbers in different Figs. refer to the same elements.

The component, which is partly shown in FIG. 1, comprises a substrate 2,for example a transparent substrate such as a glass or atransparent-plastic substrate. The upper side of the substrate isprovided with first and second electrodes 4 and 6, respectively and withbendable nano-elements 8, which are arranged between the electrodes. Theelectrodes 4 and 6 may be interdigitated, i.e. portions of firstelectrode are arranged between portions of the second electrode. Such anelectrode structure is very suitable to produce a diffraction grating,whereby the strips with bendable nano-elements form grating strips andthe electrode portions the intermediate strips. The electrodes 4 and 6shown in FIG. 1 has four fingers and three fingers, respectively.However, the number of fingers can be chosen freely and in practice willbe much larger for a diffraction grating. The electrodes are transparentand may be made of, for example indium tin oxide (ITO).

As shown in the cross-section view of FIG. 2, the electrodeconfiguration 4,6 may be covered by a dielectric layer 10, for example aSiO₂ layer. This layer can be coated by a sol-gel technique, whereby asolution of tetraethoxyorthosylicate is applied and subsequently cured.The dielectric layer 10 has a double function. Firstly, it provides aplanar surface for the nano-elements, which simplifies placing thebendable nano-elements 8 in position afterwards. Secondly it forms aninsulating layer between the electrodes 4, 6 and the nano-elements. Inthis way, the position of the nano-elements, straight or curved, will bedetermined by the electrical or magnetic field, and not by directcontact with the electrodes. The dielectric layer 10 can be supplied bychemical vapour deposition or any other deposition method. In case sucha deposition method does not result in a planar layer surface, anadditional planer layer may be supplied.

In this embodiment the nano-elements 8 are carbon nanotubes, which havebeen functionalised with Si(OR)₃, groups, wherein R is methyl.Functionalization of carbon nanotubes with suitable end groups per se isknown from the above cited paper in Langmuir, Vol 16 (2000), pp3569-3573. Therein, single walled carbon nanotubes of desired length aresuspended with ultrasonification in alcohol. The carbon nanotubes havecarboxylic acid end groups by oxidation. This end group is substitutedthrough a chemical reaction with Si(OR)₃. In order to obtain a patterneddeposition, the substrate is covered with a photoresist material, whichis developed according to the desired pattern. Then the photoresistmaterial and the substrate undergo a plasma treatment process so as tomake the substrate more hydrophilic and the photoresist morehydrophobic. A suitable treatment process is a sequence of an oxygenplasma treatment, a fluor plasma treatment and an oxygen plasmatreatment. Bundles of carbon nanotubes will align across the surface dueto the hydrophobic interactions between the individual carbon nanotubes.

Instead of by means of a photoresist, a mask of another material may beused to obtain the required pattern. The pattern may also be obtained byburning away carbon nanotubes from portions of the surface, for exampleby means of a laser beam having sufficient intensity.

The resulting component is a transmission component, as shown in FIG. 2.A beam of radiation b passes the component unhindered, because thenanotubes are aligned parallel to the propagation direction of theradiation, which in this case is perpendicular to the surface. This isthe case if no voltage is supplied to the electrodes, i.e. no electricalfield is present. If the electrical field is switched on, thenano-elements will bend and become curved elements 8′, as shown in FIG.3. The curved nano-elements now cover at least a substantial portion ofthe areas between the electrodes 4 and 6 and absorb that component ofthe beam b that has a polarization direction parallel to the tangent ofthe curved nano-tubes. The absorption of an incident beam b will bemaximum if the beam is linearly polarized beam having its polarizationdirection tangent to the curved nano-tubes.

The nano-tubes can be bended by means of an electrical field having afield strength in the range from 0.1 to 5 Volt/μm. The voltage forgenerating the electrical field may be a DC voltage. However, it hasbeen demonstrated that for the larger values of the voltage range, thebest results are achieved if the voltage is an AC voltage, preferablyhaving a frequency in the range from a few Hz to some KHz, morepreferably about 50 Hz.

The strip shaped electrodes 4 and 6 are substantially longer than shownin FIGS. 2 and 3, i.e. their lengths is substantially larger than thedistance between them. Since these electrodes are transparent and thenano-tubes regions between them absorb radiation id the component isactivated, i.e. a driving field is present, the component acts as adiffraction grating for radiation having a suitable polarizationdirection. The particularity of this grating is that the gratingfunction can be switched on and off, simply by switching the electrical,or another driving field.

The transmission grating of FIGS. 2 and 3 can be converted into areflective grating by using a reflective substrate or by arranging areflective layer between the substrate and the electrode configuration.Alternatively both the substrate and the electrodes can be madereflective.

FIG. 4 e shows a cross-section of another embodiment of the newcomponent, which can be used as a programmable, or flexible, mask forexample in photolithography. The programmable elements, each consistingof one or two pairs of opposed electrode portions 4, 6 and nano-elementsareas there between, now constitute picture elements (pixels), whichtogether form a pattern, such as an IC pattern image that is to beprojected in a photoresist layer on top of a semiconductor substrate.The image content is determined by the state, switched on or off, of theindividual pixels. Such a pixel usually consist of one programmableelement under circumstances a pixel may comprise more than oneprogrammable element. The pixel configuration is now two-dimensional.

FIGS. 4 a-4 d shows stages in the manufacture of the component shown inFIG. 4 e. The electrodes 4 and 6 are interdigitated and each portion ofan electrode is connected with the other portions thereof, in a similarway as shown in FIG. 1. The nano-elements in this embodiment arenanowires, which have been grown electrochemically and may be arrangedin a cavity formed by a spacer 22 and a cover 24, for example ofplastics.

The bendable nanowires 26 may be supplied by means of template growth,as will be explained with reference to FIGS. 4 a-4 d. FIG. 4 a shows anintermediate product comprising some layers and produced by means of asemiconductor manufacturing technique. This product comprises asubstrate 2, for example of glass, electrodes 4 and 6 and an etch-stoplayer 28, for example of silicon nitride. The layer 28 is covered by analuminium layer 30.

FIG. 4 b shows the start of formation of pores in the aluminium layer30, by means of anodised etching of the aluminium, whereby aluminium isconverted into aluminium oxide (Al₂O₃). The anodised etching ofaluminium is a conventional technique. The pores 32 are deepened bymeans of O₂ evolution until the reach the etch stop layer 28, as shownin FIG. 4 c. This result in an aluminium layer with, for example 30%porosity. The pore density is, for example of the order of 5.10¹⁰/cm².

FIG. 4 d shows the product after some further process steps, which areknown per se, have been carried out and nanowires have been grown. Cunanowires can be grown from CuSO₄, Au nanowires can be grown fromK₄Au(CN)₃, Ni nanowires can be grown from NiSO₄/NiCl₂ and CdSe nanowirescan be grown from CdCl₂ and H₂SeO₃ in water. In the process stage shownin FIG. 4 d also the aluminium matrix has been dissolved at leastpartially. Preferably, the lower portion, some nano meters thick, of thealuminium matrix is retained. In this way an improved adhesion of thenanowires to the substrate is obtained. In order to retain the spacersof Al₂O₃, a mask is used so as to etch selectively. These spacers 22 areporous, but sufficient strong to be used as a wall.

As shown in FIG. 4 e, a cover 24 may be arranged on top of the spacer 22and attached with a glass frit. If desired the cover 24 may be providedwith an electrode layer on one of its surfaces, preferably the surfacefacing the nano-elements. This electrode may be used for quick return ofthe nanowires from the bent state into the non-bent state. Anotherelectrode may form part of the substrate. Furthermore, the cavitycontaining the nano-elements may be filled with a liquid.

Alternative methods for providing nanowires with template growth may beused as well. For example, a layer of a noble metal, such as gold orplatinum can be deposited on top of the silicon nitride layer 28. Such alayer acts as an etch stop layer and at the same time can be used as aplating base. The layer of the noble metal can be configured accordingto the required pattern and in the end be used as an additionalelectrode. In such an embodiment the layer of noble metal is presentonly in the regions between the electrodes 4, 6 and the nano-elements donot extend to the top of the electrodes.

Alternatively, the layer of noble metal, or any other metal such asnickel or copper may be removed after the nanowires have been suppliedand the aluminium matrix has been removed. This step is particularlysuitable if the nanowires comprise a semiconductor material, which hasbeen deposited electrochemically or with the VLS method. The layer ofnoble metal then can be etched selectively with respect to thenanowires, i.e. the complete regions with nanowires acts as an etchmask. The mechanical stability of the nanowires is not a specificproblem for this embodiment, because a certain mechanical stability isgenerally required when arranging bendable elements.

In an alternative embodiment the electrodes 4, 6 are moved to theopposite side and the layer of noble metal is deposited directly on topof the substrate 2. the opposite side may be the inner surface of thecover plate 24.

Most preferred is the embodiment wherein use is made of the substratetransfer method, i.e. the original substrate is finally removed and thealuminium matrix is dissolved from the substrate side instead of fromthe top side. After growing of the nanowires and before dissolution ofthe aluminium matrix, a layer of dielectric material and the electrodesare arranged on top of the matrix. This can be done by means of anythin-film process, such as wet-chemical deposition, sputtering andchemical vapour deposition. Further interconnect layers may bedeposited, as well as a protective cover layer of, for example glass ora polymer. Then the product is turned upside down and the substrate, theetch-stop layer (alias plating base) and the aluminium matrix areremoved. The glass substrate can be removed by irradiating anUV-releasable glue layer, which is arranged between the glass substrateand the etch-stop layer, with actinic UV radiation.

The pattern of nanowires can also be produced by means of a catalyticCVD growth process.

The processes described hereinabove for the production of nanowires canalso be used for the production of nanotubes.

The programmable mask of FIG. 4 e can be used with great advantage in alithographic projection apparatus. FIG. 5 shows a very schematicperspective view of such an apparatus. The main modules of thisapparatus are: an illumination system 42, a mask table 50, a projectionsystem 60 and a substrate (wafer) table 70. The illumination system 42comprises a radiation source 44, such as a Hg lamp or excimer laser, forsupplying a projection beam 46 of, for example UV radiation or extremeUV (EUV) radiation. The projection beam is guided to the mask table viafolding mirrors 47 and 48 and a diaphragm 49. The illumination beamfurther comprises means (not shown) for making the beam intensityuniform throughout its cross-section and beam shaping lenses and/ormirrors. The apparatus may also use other types of radiation such asX-rays or a charged particle beam.

The mask table 50 is provided with a mask holder 52 for holding a mask53, e.g. a reticle. This mask comprises a mask pattern that is to beprojected on the substrate by means of the projection beam 46. Thisprojection is performed by the projection system 60, which may be lenssystem, a mirror system, a system comprises lenses and mirrors, or acharged particle imaging system. The projection system images anilluminated portion of the mask 53 onto a target portion (die) 76 of thesubstrate 74. The substrate, or wafer, is accommodated in a substrateholder 72, which forms part of the substrate table 70. The substrate iscoated with a resist layer in which the image of the mask pattern isformed. In a stepper type apparatus the whole mask pattern isilluminated and projected onto a target portion 76. To expose all targetportion with the mask pattern, the substrate table is, betweensuccessive exposures, stepped, i.e. moved over predetermined distancesin the X- and Y-direction, by driving means 78, In a step-and-scanningtype apparatus a small portion (rectangular or annular segment) of themask pattern and a corresponding portion of the target are illuminatedat any time. To illuminate the whole mask pattern and to expose thewhole target portion 76, the mask table and substrate table are moved(scanned) synchronously with respect to the illumination system and theprojection system. To allow such scanning the mask table should beprovided with driving means and the driving means 78 for the substratetable should be adapted.

Conventionally the mask comprises a fixed mask, which has beenmanufactured by a mask manufacturer upon specification of the designerof the device to be manufactured and of the patterns of the differentlayers of this device. A mask is a costly component and becomesrelatively more costly if the number of devices to be manufactured bymeans of the mask decreases. Moreover in the pilot manufacture of adevice often re-design of the mask pattern is necessary, which resultsin a considerable increase of time and costs.

According to the invention the conventional mask 53 can be replaced by aprogrammable mask 20 as described herein above and by including acontrolling device 56 for this mask, as shown in FIG. 5. The controllingdevice may be a separate module, for example a microcomputer, or mayform part of the control module, which controls all functions of thelithographic apparatus. In this way, the photolithographic technologybecomes very flexible, because the mask pattern can be changed at anymoment, simply by switching on or off its individual pixels, orprogrammable elements, according to the required mask pattern. In apilot manufacturing process the mask can easily be corrected and neednot to be replaced if correction are needed. The mask is suitable forthe manufacture of very different types of devices and allowsconsiderably reducing the cost for small quantity devices such ascustomized devices.

The programmable mask can also be used in a proximity printingapparatus, wherein no projection system 60 is used and the mask and thesubstrate are separated by only a small air gap.

A special advantage of the use of the programmable mask in lithographyis that the mask is not sensitive to projection radiation, such as deepUV (DUV) radiation.

The switchable grating described hereinabove can replace a conventionalamplitude grating and shows the advantages that it is easy and cheap tomanufacture and shows a high contrast between the grating strips and theintermediate strips. The capabilities of this grating can be used to theoptimum extent in an optical system or device wherein two radiationbeams are used, which beams follow the same radiation path, whilst onlyone of the beam should undergo diffraction and the other not. This canbe achieved by arranging the novel grating in the common radiation pathand switching the grating on for one beam and off for the other beam.

An example of such an apparatus is an optical scanning device forreading and recording an optical information carrier of a first typehaving a first information density and an optical information carrier ofa second type having a second information density. This device comprisesa radiation source unit supplying a first radiation beam having a firstwavelength for cooperating with the first type of information carrierand a second radiation beam having a second wavelength for cooperatingwith the second type of record carrier and an objective system forfocussing the first and second beam in the information layer of thefirst and second type record carrier, respectively.

The published patent application US2002/0027844A1 describes an exampleof an optical scanning device for scanning in a first mode of operationa first record carrier having a first, HD, information layer and forscanning in a second mode of operation a second type of record carrierhaving a second, LD information layer, which device may comprise severaldiffraction gratings. HD stands for high density and a high-densityrecord carrier is for example a record carrier of the DVD (digitalversatile disc) type. Such a record carrier is scanned by a HD beam. LDstands for low density and a low-density record carrier is for example arecord carrier of the CD (compact disc) type. Such a record carrier isscanned by a LD beam. The HD beam has a smaller wavelength, for example650 nm, than the LD beam, for example 780 nm, so that a same objectivesystem focuses a HD beam to a smaller spot than a CD beam.

FIG. 6 shows an embodiment of such type of scanning device, which isalso called combination (combi) player. The optical path of the device80 comprises a radiation source 82 in the form of a two wavelength diodelaser package. This is a composed semiconductor module, which has twoelements 83 and 84 emitting radiation beams of different wavelengths 86and 87, respectively. This module may comprise a single diode laser chiphaving two emitting elements or two diode laser chips arranged in onepackage. Although the distance between the emitting elements is made assmall as possible, the chief rays of the beams 86 and 87 do notcoincide. Nevertheless in FIG. 6 the HD beam 86 and the LD beam 87 arerepresented by a single radiation beam for sake of clarity.

The beam 86 or 87 emitted by the radiation source unit 82 is incident ona beam splitter 88, for example a semi-transparent mirror, whichreflects part of the beam to a collimator lens 90. This lens convertsthe divergent beam into a collimated beam. This beam passes an objectivelens system 92, which focuses the HD beam to a scanning spot 94 and theLD beam to a scanning spot 96.

The HD record carrier 100 to be scanned by the spot 94 comprises atransparent layer 101 having a thickness of, e.g. 0.6 mm and aninformation layer 102. The LD record carrier 105 to be scanned by thespot 96 comprises a transparent layer 106 having a thickness of, e.g.1.2 mm and an information layer 107.

Radiation of the beam 86 or 87 reflected by the respective informationlayer returns along the optical path of this beam, passes the beamsplitter 88 and is converged by the collimator lens 90 to a spot 98 and99 respectively on a radiation-sensitive detection system 97. Thissystem converts the beam into an electrical detector signal. Aninformation signal representing information stored in the informationlayer being scanned and control signals for positioning focus 94 or 96in a direction normal to the information layer 102 or 107 (focuscontrol) and in a direction normal to the track direction (trackingcontrol) can be derived from the detector signal.

In a device of the type schematically shown in FIG. 6 diffractiongrating may be used at different positions in the radiation path and fordifferent purposes. A beam combining grating may be arranged close tothe radiation source unit 82 to diffract one of the beams 86,87 suchthat its axis coincides with that of the other beam, which is notdiffracted so that the two beams follow exact the same path in thedevice. The requirement that the grating should be effective for onlyone of the beams can be satisfied by using a grating according to theinvention and switch this grating on, i.e. bend the nano-elements inthis grating, together with the radiation source 83 or 84, whichsupplies the beam that should be diffracted. Care should be taken thatthis beam is a linearly polarized beam having its polarization directionparallel to the mean direction of a bended nano-element. FIG. 6 showssuch a schematically represented grating 110 and a line 112 between thisgrating and a control input of the source unit 82, which linesymbolically represent the simultaneous switching of the grating and therelevant radiation source.

A beam combining grating may also be arranged between the beam splitter88 and the radiation sensitive detection system 97 to diffract one ofthe beams reflected by the relevant information layer such that thisbeam becomes coaxial with the other beam reflected by the otherinformation layer. The spots 98 and 99 formed by these beams on theradiation-sensitive detection system than have the same position so thatthe same detection element can be used for the two beams. Since only oneof the beams should be diffracted and the other not, a diffractiongrating according to the invention can advantageously be used for thispurpose. Such a grating is schematically represented by element 114 inFIG. 6.

In a device of the type shown in FIG. 6 track following, i.e. keeping ascan spot on the information track that is momentarily scanned, can becarried out by means of the three-spots method. A device using thismethod comprises a diffraction grating that splits a scanning beam intoa main beam forming a main spot in the information layer and twoauxiliary beams forming two satellite spots in the information layer.The main spot is used for reading and/or recording information and thesatellite spots are used for measuring the position of the main spotwith respect to the centre line of the information track. If thethree-spots method is used for only one of the beams, for example a beamthat records information, the three spots grating should be invisiblefor the other beam. This can realized by replacing a conventionaldiffraction grating by a switchable grating according to the invention,which grating is switched off during the presence of said other beam.Such a three-spots grating 116 can be arranged between the source unit82 and the beam splitter 88. If a beam combining grating 110 is alsopresent, the gratings 110 and 116 can be arranged at different side ofone substrate 118, as shown in FIG. 6.

The device may also comprise two three-spots diffraction gratings, onefor each of the beams, for example in case the two beams should recordinformation in their respective information plane. In that case, at anytime during operation of the device one of the three-spots gratings isswitched on and the other switched off, simultaneously with the beam forwhich the grating is destined.

Two applications of the invention has been described: a programmablelithographic mask and a switchable linear diffraction grating for theoptical recording technique. This does not mean that the invention islimited to these applications. The switchable linear grating accordingto the invention can be used in any optical system wherein two beamstravelling along the same path are used, one of which has to bediffracted and the other not and, more general, in any optical systemwherein a switchable grating is used. The programmable grating may alsobe a two-dimensional grating, i.e. a grating having first grating stripsand second grating strips, which differ from each other in that theyextend in different directions, for example mutually perpendiculardirections. The first grating strips, together with their intermediatestrips, are arranged in first surface areas and the second gratingstrips, together with their intermediate strips, are arranged in secondsurface areas, which alternate with the first surface areas. The firstand second surface areas may be square-shaped and the borders of theseareas may be parallel or diagonal to the borders of the whole grating.

The invention can not only be used in a diffraction grating, but in anydiffraction element which is composed of first areas, strip- orotherwise shaped, which alternate with second areas, which first andsecond areas show different absorption. A well known example of such adiffraction element is a Fresnel (zone) lens. FIG. 7 shows an embodimentof a Fresnel lens 120 according to the invention. This lens is composedof first annular shaped strips 122, which alternate with second annularshaped strips 124. The first strips comprises nano-elements 126, whilstthe second strips do not. The nano-elements are shown in bendedposition, i.e. the lens is switched on and the first strips absorbradiation having the appropriate polarization. Since the second stripsdo not absorb radiation, the component acts as a Fresnel lens. If thecomponent is switched off, i.e. the nano-elements are orientedperpendicular to the plane of drawing, the first strips are notabsorbing and the component is a plane parallel plate. For clearnesssake only a few strips have been shown in FIG. 7, but in practice thenumber of strips may be much larger. The same holds for the number ofnano-elements. The Fresnel structure may be manufactured in the same wayas described hereinabove for the linear grating.

1. A programmable optical component for spatially controlling theintensity of a beam of radiation, which component comprises aprogrammable layer which is divided in programmable elements,characterized in that each programmable element comprises bendablenano-elements which are switchable between a non-bend state and a bendstate by means of a driver field.
 2. A component as claimed in claim 1,characterized in that it comprises a substrate, an electrodeconfiguration of first and second electrode portions, whichconfiguration defines the programmable element areas, and anano-elements embedding medium on top of the electrode configuration. 3.A component as claimed in claim 2, characterized in that an electricallyisolating layer is arranged between the electrode configuration and thenano-elements embedding medium.
 4. A component as claimed in claim2,characterized in that each nano-element is arranged in an insulatingregion.
 5. A component as claimed in claim 2, characterized in that thenano-elements embedding medium is an insulating fluid.
 6. A component asclaimed in claim 2, characterized in that the first and second electrodeportions form a pair of interdigitated electrodes.
 7. A component asclaimed in claim 2, characterized in that the electrode configuration isembedded in a planarizing layer and the nano-elements embedding layer isarranged on the planarizing layer.
 8. A component as claimed in claim 2,characterized in that a second electrode configuration is arranged atthe side of the nano-elements embedding medium remote from the mediumside facing the substrate.
 9. A component as claimed in claim 1,characterized in that the nano-elements have a diameter in the rangefrom 1 nm to 50 nm.
 10. A component as claimed in claim 1, characterizedin that the nano-elements are nanowires.
 11. A component as claimed inclaim 1, characterized in that the nano-elements are nanotubes.
 12. Acomponent as claimed in claim 1, characterized in that the nano-elementscomprise a semiconductor material.
 13. A component as claimed in claim11, characterized in that the nanotubes are carbon nanotubes.
 14. Acomponent as claimed in claim 13, characterized in that the nanotubesare single wall nanotubes.
 15. A component as claimed in claim 1,characterized in that it is a transmission component.
 16. A component asclaimed in claim 1, characterized in that it is a reflective component.17. A component as claimed in claim 1, forming a switchable diffractiongrating, wherein the programmable elements have an elongated shape andconstitute grating strips, which alternate with nano-elements lessintermediate strips.
 18. A component as claimed in claim 17, forming alinear grating, wherein the programmable elements all extend in the samedirection.
 19. A component as claimed in claim 17, forming atwo-dimensional grating having first programmable element extending in afirst direction and second programmable elements extending in a seconddirection, different from the first direction, which first programmableelements are arranged in first surface areas and which secondprogrammable elements are arranged in second surface areas alternatingwith the first surface areas.
 20. A component as claimed in claim 1,forming a switchable Fresnel lens, wherein the programmable elementshave an annular shape and constitute Fresnel lens zones, which alternatewith nano-elements less intermediate annular strips.
 21. A component asclaimed in claim 1, forming a mask having a changeable mask pattern,wherein the programmable elements constitute pixels, which are arrangedin a two-dimensional structure.
 22. A device for scanning an opticalinformation carrier of a first type having a first information densityand an optical information carrier of a second type having a secondinformation density, which device comprises a radiation source unitsupplying a first radiation beam having a first wavelength forcooperating with the first type information carrier and a secondradiation beam having a second wavelength for cooperating with thesecond type of record carrier, and an objective system for focussing thefirst and second beam to a first and second scanning spot in theinformation layer of the first and second type information carrier,characterized in that it comprises at least one component as claimed inclaim
 18. 23. A device as claimed in claim 22, characterized in that thecomponent is a beam-combining diffraction grating and in that such agrating is arranged in at least one of the following optical pathportions: between the radiation source unit and the objective system,between the objective system and a radiation-sensitive detection systemfor receiving radiation from the information layers.
 24. A device asclaimed in claim 22, characterized in that the component is athree-spots diffraction grating and is arranged between the radiationsource unit and the objective system.
 25. A lithographic process forproducing device features in at least one layer of a substrate, whichprocess comprises transferring a mask pattern into the substrate layerby means of a projection apparatus, characterized in that use is made ofa mask as claimed in claim 21.